Abstract
In temporal discounting, animals trade off the time to obtain a reward against the quality of a reward, choosing between a smaller reward available sooner versus a larger reward available later. Similar discounting can apply over space, when animals choose between smaller and closer versus larger and more distant rewards. Most studies of temporal and spatial discounting in non-human animals use food as the reward, and it is not established whether animals trade off other preferred stimuli in similar ways. Here, we offered female guppies (Poecilia reticulata) a spatial discounting task in which we measured preferences for a larger reward as the distance to it increased relative to a closer but smaller reward. We tested whether the fish discounted reward types differently by offering subjects either food items or same-sex conspecifics as rewards. Before beginning the discounting tasks, we conducted validation tests to ensure that subjects equally valued the food and social stimuli in the quantities provided. In the discounting task, subjects switched their preferences from the larger to the smaller reward as the distance to the larger reward increased (spatial discounting), but the pattern and magnitude of discounting did not differ across the two reward types. These findings indicate that guppies show similar patterns of discounting for food and social rewards in a spatial task. In an examination of travel times, however, the fish swam faster to food rewards than to shoaling partners. Analysis of travel times suggests that fish temporally discounted social rewards less steeply than food rewards. Thus, reward type influences temporal discounting, suggesting a dissociation between temporal and spatial discounting. Our results illustrate how animals adjust choices and travel times depending on both the type of cost (time, distance) and benefits (food, social partners).
Highlights
Chacma baboons (Papio ursinus) in South Africa will walk by less desirable food patches on the way to more desirable food (Noser and Byrne, 2007)
Before beginning the discounting tasks, we conducted validation tests to ensure that subjects valued the food and social stimuli in the quantities provided. Subjects switched their preferences from the larger to the smaller reward as the distance to the larger reward increased, but the pattern and magnitude of discounting did not differ across the two reward types. These findings indicate that guppies show similar patterns of discounting for food and social rewards in a spatial task
Analysis of travel times suggests that fish temporally discounted social rewards less steeply than food rewards.reward type influences temporal discounting, suggesting a dissociation between temporal and spatial discounting
Summary
Chacma baboons (Papio ursinus) in South Africa will walk by less desirable food patches on the way to more desirable food (Noser and Byrne, 2007) This phenomenon represents a case of spatiotemporal choice, in which the baboons choose a higher quality reward delayed in time and at a greater distance over a lower quality, immediate reward. Researchers have studied the temporal component of these choices (termed intertemporal choice) in a number of animal species, including honeybees, pigeons, starlings, chickens, blue jays, parrots, rats, monkeys, and apes (Ainslie, 1974; Bateson and Kacelnik, 1996; Tobin et al, 1996; Richards et al, 1997; Stephens and Anderson, 2001; Cheng et al, 2002; Green et al, 2004; Abeyesinghe et al, 2005; Stevens et al, 2005a; Evans and Beran, 2007; Rosati et al, 2007; Pearson et al, 2010; Vick et al, 2010). The decision context can influence temporal preferences, and animals often employ ecologically rational decision strategies (Todd and Gigerenzer, 2007), depending on the environment
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